The present application relates to optical grating assemblies, and more particularly to an assembly and method for a configurable grating assembly based on a surface relief pattern for use as a variable optical attenuator.
Fiber networks normally employ point-to-point links, which are static, where most of the intelligence, provisioning and grooming functions are provided by electronics at the ends of each link. As network architectures grow in size and complexity, however, this approach to building and maintaining network infrastructure will not satisfy the requirements of reliability, efficiency and cost-effectiveness required by service providers. Therefore, the industry is moving to optically reconfigurable networks where optical paths, wavelengths and data rates are dynamically changed to satisfy network system requirements, such as provisioning new wavelengths, balancing data loads and restoring after-service malfunctions.
Variable optical attenuators (VOA) are used to permit dynamic control of optical power levels throughout a network. As an example of their usefulness, if a network is providing a wavelength route that is approximately 60 km in length, at a predetermined power, and the network attempts to change the wavelength route to one which is 30 km, it would be expected that excessive power would be delivered to the end receivers of the 30 km route, potentially resulting in a malfunction in the network. A VOA will lower the power output of the switched wavelength to permit a signal of acceptable strength at the end receiver. Existing VOAs implement mechanical systems to attenuate the light. In one design, attenuation is accomplished by moving two separate optical fibers, and in another by inserting a motor-driven blade or filter in the light path. While these devices have acceptable optical performance, tradeoffs include slow speed, undesirable noise and a potential for mechanical failure.
It has been appreciated by the inventors, that systems now exist which describe structures incorporating deformed/deformable structures for light modulation.
Sheridon, in an article entitled, “The Ruticon Family of Erasable Image Recording Devices,” IEEE Transactions on Electron Devices, ED-19, No. 9, September 1972, pp. 1003-1010, teaches Ruticons are solid-state cyclic image recording devices. They have a layered structure consisting of a conductive transparent substrate, a thin photoconductive layer, a thin deformable elastomer layer, and a deformable electrode such as a conductive liquid, a conductive gas, or a thin flexible metal layer. When an electric field is placed between the conductive substrate and the deformable electrode the elastomer will deform into a surface relief pattern corresponding to the light-intensity distribution of an image focused on the photoconductor. Light modulated by the deformation of the elastomer surface can in turn be converted to an intensity distribution similar to the original image by means of simple optics. Ruticons are expected to find initial applications in image intensification, holographic recording, and optical buffer storage.
Further, in “The Optical Processing Capabilities of the Ruticon,” SPIE Vol. 128, Effective Utilization of Optics in Radar Systems (1977), pp. 244-252, Sheridon, et al. teach the Ruticon is a solid state optical image modulator consisting of a metallized elastomer layer coated on a photoconductor layer. An electrical field is placed between the metal surface and a transparent conductive substrate. An input image, such as from a CRT or a laser, causes a change in the distribution of electrical fields across the device, and the mechanical forces associated with these electrical fields cause the metallized elastomer surface to deform into an image pattern. Laser light reflected from this surface is phase modulated with the input image information and this modulated light may be used as the input to a coherent optical processing system.
Other examples of such designs include two patents to Glenn, U.S. Pat. Nos. 4,529,620 and 4,626,920. These patents disclose the generation of video imagery through the use of storing a charge pattern representative of a video frame. The system employs a solid state light modulator structure having an array of space charge storage electrodes. An elastomer layer is disposed on the semiconductor device, over the array of charged storage electrodes. At least one conductive layer is disposed over the elastomer layer. The semiconductor device is responsive to the input video signal to selectively apply voltage between the charged storage electrodes and the one conductive layer to cause deformations of the conductive layer and the elastomer layer. A plastic pellicle layer may be disposed between the elastomer layer and the at least one conductive layer. These patents are hereby incorporated by reference in their entirety.
Laude et al., U.S. Pat. No. 3,942,048, is directed to an optical grating assembly having a piezoelectric substrate, which supports, on two opposite faces thereof, respective metallic layers. One of these faces of the substrate also carries a grating. Application of a variable voltage between the metal layers sets up an electric field of variable strength in the substrate, resulting in the pitch of the grating being variable due to the piezoelectric nature of the substrate. Laude et al. '048 is incorporated by reference in its entirety.
Bloom et al., U.S. Pat. No. 5,459,610, describes a modulator for modulating incident rays of light. The modulator includes a plurality of equally spaced apart beam elements, each of which includes a light-reflective planar surface. The elements are arranged parallel to each other with their light reflective surfaces parallel to each other. Means are provided for supporting the beam elements in relation to one another. Additional means are provided to the beam elements relative to one another so that the beams move between a first configuration wherein the modulator acts to reflect the incident rays of light as a plane mirror, and a second configuration wherein the modulator diffracts the incident rays of light as they are reflected. Bloom et al. '610 is hereby incorporated by reference in its entirety.
An article by Kück et al., entitled “Deformable Micromirror Devices as Phase-Modulating High-Resolution Light Valves,” Sensors and Actuators A 54 (1996) 536-541, reports on two different technologies for deformable micromirror devices as phase-modulating light valves for high-resolution optical applications. Disclosed is a fabricated light valve with CMOS addressing and viscoelastic layer deformable mirrors. On top of a substrate carrying pixel electrodes is the viscoelastic control layer covered with a mirror electrode. A bias voltage of typically 250 V is applied between the pixel electrodes and the mirror electrode, whereby the reflective viscoelastic layer behaves like a plane mirror. On applying a single voltage of about ±15 V to neighboring pixel electrodes, the viscoelastic mirror is deformed sinusoidally forming a phase grating corresponding to the active pixels. In order to avoid the imprinting of an image pattern into the viscoelastic layer, the polarity of the signal voltage is changed in subsequent image cycles. Kück et al. is hereby incorporated by reference in its entirety.
The foregoing material does not address the noted shortcomings, and further fails to disclose a VOA, which also permits for analog control and for specific configurations.